1. Field of the Invention
The present invention relates to a resistor and electrodes formed on a substrate and which is coated with a glass layer and particular wherein said resistor and electrode is useable in an electron gun of a television set.
2. Description of the Prior Art
In a conventional color television picture tube, a high voltage such as 25.about.30 KV is applied to the last accelerating electrode of an electron gun unit and a picture screen through an anode button mounted at the funnel portion of a picture tube. At the same time, a voltage of 0.about.5 KV is applied to a focusing electrode forming a focusing electron lens positioned near the last accelerating electrode, through a terminal pin provided at the end of a neck portion of the picture tube.
In order to make a small beam spot on the picture screen which results in a more precise and clear picture, it is desirable to reduce the aberration of the focuing lens as much as possible. To reduce the aberration of the focusing lens, it is necessary to relax the voltage gradient between the electrodes. To achieve this, there are such methods as widening the distance between the electrodes, applying close voltage to the electrodes, and a combination of the above.
In the case of applying a similar voltage to the electrodes, it is necessary to apply a high voltage of more than 10 KV to the focusing electrode next to the last accelerating electrode. Such high voltage cannot be applied through a terminal pin provided at the end of the neck portion of the picture tube, because there occurs an electric discharge (spark) between the terminal pin and the other terminal pins which supply voltage to other electrodes of the electron gun unit, for example, heaters. Then, it can be supplied through another button provided at the funnel portion, however, it causes complicated assembly and a substantial cost-up.
In the case of a picture tube widely known as a "Trinitron" (registered Trademark of Sony Corporation, the assignee of the present invention), three electron beams are focused by a single electron lens, in which each beam passes through the center of a single electron lens of large diameter. The focused three electron beams are deflected to hit the same position of an apertured grille provided in front of the picture screen by four convergence electrodes provided at the top end of the electron gun unit which makes three passages therebetween for each of the electron beams. Two inner electrodes of the convergence electrode are applied by the same potential as the anode potential. Two outer electrodes of the convergence electrodes are applied by a lower voltage than the anode potential by 0.4.about.1.5 KV, so that the electron beams which pass through the convergence electrodes are deflected to the side of the center beam.
At one time, the voltages were applied through another button provided at the funnel portion and an electrically shielded cable connected to the button and the outer electrodes.
Now, a co-axial anode button, which has two cylindrical electrodes electrically insulated from each other, is used to provide an anode voltage through an outer electrode of the anode button, and convergence voltage through an inner electrode of the anode button and an electrically shielded cable connecting the inner electrode and the convergence electrodes. By the above co-axial anode button, it is not necessary to provide two buttons at the funnel portion of the picture tube, however, still it is troublesome to connect the inner electrode of the anode button and outer convergence electrodes by the electrically shielded cable.
Other specific disclosures of possible interest are Japanese Publication 40987/72 and U.S. Pat. No. 3,514,663, both assigned to the same assignee as the present invention and U.S. Pat. No. 3,932,786.